1. Field of the Invention
The present invention relates to a semiconductor device including a capacitor and a method of manufacturing the same.
2. Description of Related Art
Along with the spread of mobile terminals, such as mobile phones, demands for low power consumption on semiconductor devices mounted on mobile terminals have been increasing, and operating power source voltage of the semiconductor device tends to be lowered. Because of the need to ensure a stable low voltage supply, a power supply line in the semiconductor device is provided with a compensation capacitance element.
A technique of applying capacitors as compensation capacitance elements having the same structure as that in a memory cell region is disclosed in JP2010-67661A. As with the technique of JP2010-67661A, application of capacitors having a three-dimensional structure for memory cells allows the layout area of compensation capacitance element to be reduced.
Application of crown capacitors to capacitors of a compensation capacitance element allows the area of a region in which the compensation capacitance element is formed (hereinafter, referred to as compensation capacitance region) to be further reduced. However, there is a possibility that the crown capacitors will be destroyed during the manufacturing process. In order to address this problem, an example of a technique of preventing crown capacitors from being destroyed is disclosed in JP2003-297952A. The technique disclosed in JP2003-297952A prevents the crown lower electrode in the manufacturing process from being destroyed, by means of guard rings and a support film.
In order to further reduce the area of the compensation capacitance region, a structure that supports capacitors only by a support film connecting the capacitors without providing any guard ring has been examined.
In a memory cell region, a multiplicity of crown electrodes are arranged in one integrated region. Accordingly, only connection by a support film can prevent the capacitor from being destroyed. On the other hand, also in a compensation capacitance region, although the number of capacitors is smaller than that in the memory cell region, arrangement of about ten thousands of capacitors can prevent the capacitors from being destroyed only by connection of a support film without any guard ring. The crown capacitor formed without any guard ring is hereinafter referred to as a crown capacitor with a guard ring-less structure.
The inventor of the present application has examined applying the crown capacitor with a guard ring-less structure to a compensation capacitance element, and thereby discovered that there is a problem which differs from the problem in which capacitors get destroyed. Through a process of manufacturing the crown capacitors, the problem will hereinafter be described.
The process of manufacturing the crown capacitor is simply described in a manner separated into seven steps: (1) after elements, such as MOS transistors, are formed on a semiconductor substrate, an oxide film for forming cylinders (hereinafter, referred to as core oxide film) is formed on the semiconductor substrate; (2) a nitride film is formed as a support film on the core oxide film; then, (3) cylinder holes are formed at the core oxide film and the support film, and subsequently; (4) the walls of the cylinder holes are covered with conductive films and thereby cylinder-type lower electrodes are formed; (5) the support film is patterned to form opening patterns arranged on the support film at certain intervals; further, (6) wet etching is performed, masked with the support film, and the core oxide film is removed; and subsequently (7) the exposed surfaces of the cylinder-type lower electrodes are covered with a capacitance film, and a conductive film is embedded in gaps between the cylinder-type lower electrodes, thereby forming upper electrodes.
Between the steps (6) and (7), in order to wash chemical solution of the wet etching, a cleaning step is performed on the semiconductor substrate. During the cleaning step, the cylinder-type lower electrode is required not to be destroyed. During the cleaning step, a stream of water applies a lateral force to the cylinder-type lower electrodes. However, the tops of the cylinder-type lower electrodes are connected to each other by the support nitride film. This can prevent the cylinder-type lower electrodes from separately being destroyed.
On the other hand, at lower parts of the cylinder-type lower electrodes, the bottoms of the cylinder-type lower electrodes contact only pads. In comparison with the memory cell region, the area of the mat corresponding to the bottom pattern of the cylinder-type lower electrodes in the compensation capacitance region is small. Accordingly, the force that brings the cylinder-type lower electrode into intimate contact with the lower layer is small. There is the possibility of the danger that the processed film, in the area where the lower electrodes have been formed, may peel off. The peeling of the processed film is referred to as “mat skipping”, which causes the problem in which the compensation capacitance element is not formed.